1. Field of the Invention
The present invention relates to a resonator, and more specifically, the present invention relates to a resonator used for a voltage controlled oscillator or other electronic device.
2. Description of the Related Art
FIG. 5 is a schematic representation showing an example of a voltage controlled oscillator including a conventional resonator. A voltage controlled oscillator 1 includes a dielectric substrate 2. A grounding conductor layer 3 is disposed on the lower surface of the dielectric substrate 2. A microstrip line 4 is disposed on the upper surface of the dielectric substrate 2, and a resonator includes the dielectric substrate 2, the grounding conductor layer 3 and the microstrip line 4. In addition, a plurality of electronic component elements 5 are mounted on the surface of the dielectric substrate 2. The voltage controlled oscillator 1 includes these electronic component elements 5 and the resonator. In such a resonator, the frequency can be adjusted by cutting the microstrip line 4.
Further, as shown in FIGS. 6 and 7, the resonator can be defined by the grounding conductor layer 3, the dielectric layer 6 and a strip line 7 by including the multilayer substrate having two grounding conductor layers 3 and a plurality of dielectric layers 6, and laminating the strip line layer 8 defining the strip line 7 between the two grounding conductor layers 3. In this case, a circuit defined by the electronic component elements 5 mounted on the surface of the multilayer substrate is connected to the strip line 7 via a through hole 9.
The size and profile of elements and modules, including, for example, voltage controlled oscillators, used in portable terminals have been reduced, and it has been difficult to reliably provide a sufficient pattern area of the microstrip line pattern provided on the surface of the substrate with the electronic component elements mounted thereon. On the other hand, in the strip line resonator shown in FIG. 6, there are no problems with ensuring the pattern area of the strip line. However, there are structural problems in which the Q factor is low, and the C/N and S/N characteristics are degraded compared with the microstrip line resonator disposed on the substrate surface. Further, the technology to cut the strip line disposed in an intermediate layer of the multilayer substrate is required to adjust the frequency.
Also, if a conductor layer is provided inside the substrate in the microstrip line resonator, the space between the microstrip line and the conductor layer inside the substrate is reduced, and the thickness of the dielectric layer therebetween is also reduced. As a result, the Q factor of the microstrip line resonator is degraded thereby. If the thickness of the inside dielectric layer is increased to prevent such degradation of the Q factor, a problem occurs in that the thickness of the substrate must be increased and cannot satisfy the low profile requirement.